1. Field of the Invention
This invention relates generally to a sensor for use in precision farming. More particularly, but not by way of limitation, the present invention relates to an optical spectral reflectance sensor and controller for use in a site specific fertilization system.
2. Background
xe2x80x9cPrecision farmingxe2x80x9d is a term used to describe the management of intrafield variations in soil and crop conditions. xe2x80x9cSite specific farmingxe2x80x9d, xe2x80x9cprescription farmingxe2x80x9d, and xe2x80x9cvariable rate application technologyxe2x80x9d are sometimes used synonymously with precision farming to describe the tailoring of soil and crop management to the conditions at discrete, usually contiguous, locations throughout a field. The size of each location depends on a variety of factors, such as the type of operation performed, the type of equipment used, the resolution of the equipment, as well as a host of other factors. Generally speaking, the smaller the location size, the greater the benefits of precision farming, at least down to approximately one square meter.
Typical precision farming techniques include: varying the planting density of individual plants based on the ability of the soil to support growth of the plants; and the selective application of farming products such as herbicides, insecticides, and, of particular interest, fertilizer.
In contrast, the most common farming practice is to apply a product to an entire field at a constant rate of application. The rate of application is selected to maximize crop yield over the entire field. Unfortunately, it would be the exception rather than the rule that all areas of a field have consistent soil conditions and consistent crop conditions. Accordingly, this practice typically results in over application of product over a portion of the field, which wastes money and may actually reduce crop yield, while also resulting in under application of product over other portions of the field, which may also reduce crop yield.
Perhaps even a greater problem with the conventional method is the potential to damage the environment through the over application of chemicals. Excess chemicals, indiscriminately applied to a field, ultimately find their way into the atmosphere, ponds, streams, rivers, and even the aquifer. These chemicals pose a serious threat to water sources, often killing marine life, causing severe increases in algae growth, leading to eutrophication, and contaminating potable water supplies.
Thus it can be seen that there are at least three advantages to implementing precision farming practices. First, precision farming has the potential to increase crop yields, which will result in greater profits for the farmer. Second, precision farming may lower the application rates of seeds, herbicides, pesticides, and fertilizer, reducing a farmer""s expense in producing a crop. Finally, precision farming will protect the environment by reducing the amount of excess chemicals applied to a field which may ultimately end up in a pond, stream, river, and/or other water source.
Predominately, precision farming is accomplished by either: 1) storing a prescription map of a field wherein predetermined application rates for each location stored for later use; or 2) by setting application rates based on real-time measurements of crop and/or soil conditions. In the first method, a global positioning system (GPS) receiver, or its equivalent, is placed on a vehicle. As the vehicle moves through the field, application rates taken from the prescription map are used to adjust variable rate application devices such as spray nozzles. A number of difficulties are associated with the use of such a system, for example: due to the offset between the GPS receiver and the application element, the system must know the exact attitude of the vehicle in order to calculate the precise location of each nozzle or application element, making it difficult to accurately and precisely treat the target area; soil and plant conditions must be determined and a prescription developed and input prior to entering the field; and resolving a position with the requisite degree of accuracy requires relatively expensive equipment.
In the latter method, a sensor is used to detect particular soil and plant conditions as the application equipment is driven through the field. The output of the sensor is then used to calculate application rates and adjust a variable rate applicator in real time. Since the physical relationship between the sensor and the applicator is fixed, the problems associated with positional based systems (i.e., GPS) are overcome. In addition, the need to collect data prior to entering the field is eliminated, as is the need for a prescription map.
The limiting factor, thus far, in the later method has been the degree to which sensors are available which provide meaningful information concerning conditions within the field. For example, U.S. Pat. No. 5,585,626 issued to Beck et. al., and U.S. Pat. No. 5,763,873, likewise issued to Beck et al., discloses a sensor which detects plants in a field so that herbicide may be selectively applied to unwanted, plants. Unfortunately, these devices discriminate only between soil and a plant. Thus, as a sprayer is passed over areas where there should only be bare soil, herbicide will automatically be applied to any plants detected. In practice, the sensors of the Beck ""626 and ""873 patents have proven to be temperature sensitive and thus, to require nearly continuous monitoring and regular re-adjustment while being used. Furthermore, due to the nature of these devices, the distance between the sensor and the ground must be maintained with a relatively high degree of precision. Another limitation is that presently, no such sensor exists for the application of nitrogen fertilizer.
Thus it is an object of the present invention to provide a sensor for use in precision farming which provides an output indicative of one or more growing conditions over a relatively small area, which may be used for the selective application of a farming product or used in the development of a prescription map.
The present invention provides a sensor for use in precision farming which satisfies the needs and overcomes the problems discussed above. The sensor measures the reflectance of a target at one or more wavelengths of light and, based on known reflectance properties of the target, produces an output indicative of the need for a given farm product.
In a preferred embodiment, the sensor comprises: a light emitter which provides one or more light sources, each source producing light at a specific wavelength; a modulator for modulating each light source at a particular frequency, a reflected light receiver for receiving, detecting, and discriminating each wavelength of light; a direct receiver for receiving light directly from each source; and a processor for gathering information from the receivers and processing such information to determine reflectance of a plant and to determine the need for a given product based on the reflectance information.
The reflectance properties of a target are known to vary based on the amount of nitrogen available to the plant. By observing the reflected light, at particular wavelengths, preferably in the ranges of red and near infrared, and the intensity of the light source at the same wavelengths, it is possible to predict, with a reasonable degree of certainty, the expected crop yield with the present level of available nitrogen and the maximum crop yield if an ideal amount of nitrogen fertilizer is added. This information may be used in real time to control a variable rate applicator for applying a mid-growing season nitrogen fertilizer or, alternatively, used to develop a prescription map for later application of mid-growing season nitrogen fertilizer to a field. Although the inventive sensor could be easily adjusted for any particular target size, the preferred embodiment allows precision farming of sites having an area of approximately four square feet.
Another feature of the inventive device is that the accuracy of the resulting measurement is relatively independent of the height of the sensor above the ground. Thus, as a vehicle equipped with the sensor moves through a field, the output of the sensor is consistent regardless of the terrain and its effect on the height of the sensor.
Further objects, features, and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments.